1. Field of the Invention
The invention relates to receivers used for signals having multipath corrupted phase properties and with distortion caused by overlapping of adjacent data pulses.
2. Description of the Prior Art
A differentially adaptive communications system was described in U.S. Pat. No. 3,794,921 issued Feb. 26, 1974 to Manfred G. Unkauf and assigned to the present assignee, the disclosure of that patent being herein incorporated by reference.
Within the referenced patent is described a communications system for improved reception of signals which were transmitted through communications channels having multipath distortion characteristics. Within that system, a reference signal is produced in the receiver which has the same complex envelope as that of the received signals over a number of received pulses. The reference is used in a coherent matched filter-type detector employing decision feedback to permit coherent detection of the signals without the use of channelizing filters for systems employing multiple phase state digital signal modulation. Although the referenced system was capable of operating with signals from a plurality of channels, it was required that there be no appreciable overlap between adjacent pulses within any one channel in order to produce a valid determination of the phase state of pulses within any channel. Intersymbol interference caused by overlapping of adjacent pulses in the previously disclosed system and in other such communications systems reduced the signal levels within the receiver for some pulses and increased the level for others. For pulses in which the signal amplitude was lowered, the amplitude was often insufficient to permit a valid determination of the phase state of that pulse. Consequently, the system had to be operated with sufficient time spacing between adjacent bits that no overlapping could occur for any possible channel conditions. Hence, the data rate for any one channel was appreciably lowered due to the non-overlapping requirement.